A conventional outdoor unit of an air conditioner is configured to include an air blower compartment in which an air blower fan is disposed, a machine compartment in which a compressor unit, a refrigerant pipe group, and an electrical-part storage are disposed, and a partition plate that separates the air blower compartment and the machine compartment. When a function is to be added to the outdoor unit configured as described above or when the outdoor unit configured as described above controls greater performance than that of a conventional outdoor unit, it is necessary to install additional parts corresponding to the additional function or the performance. In order to ensure the space for the additional parts as described above to be installed, it is necessary to increase the size of the control board or add an auxiliary board separate from the control board. In the case where the size of the control board is increased, it is necessary to change peripheral parts around the control board, such as a side plate, a top plate, and a casing that constitute the outdoor unit. This means that these parts cannot be standardized and thus the productivity and serviceability degrade.
In order to solve the problems as described above, the structure of a conventional outdoor unit is disclosed in Patent Literature 1 listed below in which a protective cover that covers the control board is provided from the viewpoint of protecting workers, and an auxiliary board on which control elements are mounted is attached to the outer surface of the protective cover.